1. Field of the Invention
This invention pertains to an abrasive article comprising a plurality of abrasive particles and a clay-modified binder. The addition of the clay allows the binder to exhibit a controlled rate of erosion.
2. Background Art
Abrasive articles typically comprise a plurality of abrasive particles and a binder. In coated abrasives the binder is coated onto a backing, and the binder may comprise conventional make and size resins which bond abrasive particles to the backing, or the abrasive particles may be dispersed in a slurry which is coated onto a backing. In nonwoven abrasives, the binder bonds abrasive particles to the fibers of a nonwoven fibrous substrate.
In both coated and nonwoven abrasives, the binder may comprise a resinous adhesive (referred to hereinafter as simply "resin"), and optionally other additives, such as inorganic fillers. Examples of typical resins include phenolic resins, aminoplast resins, urethane resins, epoxy resins, and the like.
Typically, during the manufacture of a coated abrasive article, the resin is applied in a liquid state and subsequently solidified or cured. This curing process is usually accomplished by exposing the resinous adhesive to an energy source such as thermal energy, or radiation energy such as electron beam, ultraviolet (UV) light or visible light. In recent years, UV light curable resinous adhesives have become of interest due to the several advantages over thermally curable adhesives. These advantages include considerably faster cure times, lower capital investments and lower energy costs.
U.S. Pat. No. 2,322,156 (Oglesby) discloses the use of fillers in glutinous and resinous adhesives to improve the resulting binder's hardness, heat resistance and moisture resistance and to lower their overall cost. This patent refers to typical fillers as being inert, relatively nonabsorbent, nonfibrous, hard, dense, inelastic and nondeformable materials.
More recent patents disclose use of various radiation-cured resins but do not appreciate the interference that clays present to efficient radiation curing.
U.S. Pat. No. 4,318,766 (Smith) discloses photocopolymerizable compositions which may contain "conventional non-basic fillers (e.g., silica, talc, glass, glass bubbles, clays, powdered metal such as aluminum, zinc oxide, etc.) up to about 50% by volume or more." However, this patent does not mention the effect clay fillers might have on curing of radiation-curable binders.
U.S. Pat. No. 4,642,126 (Zador et al.) pertains to a lapping film containing a blend of a radiation curable resin and abrasive grains coated preferably on a film substrate.
U.S. Pat. No. 4,644,703 (Kaczmarek et al.) discloses a lapping film type abrasive product designed for fining plastic ophthalmic lenses. Radiation curable acrylates are disclosed, and the patentees state that the preferred abrasive grains are white aluminum oxide for its ability to transmit UV radiation. Fillers must be selected with UV absorbance in mind, and listed as preferred fillers are silica and calcium sulfate, although no filler is used in the examples.
U.S. Pat. No. 4,735,632 (Oxman et al.) discloses the use of a visible light photoinitiator with any free-radically polymerizable resin as a binder for coated abrasives. The patent states generally that inorganic or organic fillers may be used, and Example 5 discloses using a radiation curable binder resin filled 50% with calcium carbonate.
U.S. Pat. No. 4,751,138 (Tumey et al) pertains to electromagnetic radiation curable resin systems for coated abrasives. The binder contains either a physical mixture of materials having 1,2-epoxide groups and materials having ethylenically unsaturated groups, or materials having both groups on the same compound. Fillers which apparently may be utilized include kaolin clay; however, only quartz is used as filler in the examples of this patent, perhaps because of its transparency.
U.S. Pat. No. 4,773,920 (Chasman et al) discloses a lapping film abrasive product comprising abrasive grains and a free radical curable resin. No use of fillers is mentioned in the patent.
U.S. Pat. No. 4,903,440 (Larson et al.) discloses the use of an aminoplast resin having at least 1.1 pendant alpha, beta unsaturated groups as a binder resin for coated abrasives. Larson et al. also mention kaolin clay as a possible filler, however an aminosilane-treated calcium metasilicate filler is used in the examples of this patent.
U.S. Pat. No. 4,927,431 (Buchanan et al.) pertains to a coated abrasive binder containing a blend of thermally curable and radiation curable resins. The patent is devoid of disclosure or teaching of the use of clays as fillers.
U.S. Pat. No. 5,011,513 (Zador et al.) discloses a coated abrasive especially designed for lens fining applications. The coated abrasive comprises a substrate, a radiation cured make coating, abrasive grains and a radiation cured size coating. Zador et al. point out that fillers may, and preferably are used; however, the filler must exhibit low optical absorption, so as to not unduly interfere with the UV light curing. Thus, this reference teaches away from the use of low transmittance fillers (i.e., those providing a make coating with less than about 70% transmittance).
U.S. Pat. No. 5,014,468 (Ravipati et al.) pertains to a lapping abrasive article intended for ophthalmic applications. The lapping film comprises a patterned surface coating of abrasive grains dispersed in a radiation cured resin. Although the patent mentions that the abrasive grains must be selected to allow adequate curing by electron beam and UV radiation, and that white aluminum oxide (a low absorber of UV radiation) is thus preferred, there is no disclosure or suggestion of the use of clay fillers in the binders.
U.S. Pat. No. 5,152,917 (Pieper et al.) discloses an abrasive article having as its abrasive surface a plurality of precisely shaped abrasive composites. The abrasive composites comprise abrasive grains, a binder and optionally a filler. No suggestion of the use of clay fillers is given, nor the advantages or disadvantages of using clay fillers.
Patents which appear to be concerned with erodability of binders but do not discuss clays and their possible effect on binder erodability are the following patents.
U.S. Pat. No. 2,806,772 (Robie) discloses an abrasive body comprising a brittle, porous, pore support, abrasive grains and an organic binder. The porous support may be individual small thin-walled balloons of vitrified clay material described in U.S. Pat. No. 2,676,892 (McLaughlin). Use of addition polymerizable organic binders are not disclosed.
U.S. Pat. No. 4,588,419 (Caul et al.) discloses the use of calcium carbonate, aluminum silicate, alumina trihydrate, and fumed silica as fillers in radiation curable resins incorporated into coated abrasives to impart good rheological properties to an uncured binder and to promote flexibility and strength to the cured resins. Clay is not disclosed, nor its effect on erodability of addition polymerized binder resins.
U.S. Pat. No. 4,652,275 (Bloecher et al.) discloses erodible abrasive grain agglomerates comprising abrasive grains, a thermoset binder and a matrix material selected from wood pulp, wood flour and vermiculite. The matrix material renders the abrasive agglomerates erodible. There is no disclosure of clay or addition polymerizable binder resins.
U.S. Pat. No. 4,871,376 (DeWald) pertains to a coated abrasive binder comprising a resinous adhesive, filler, and a coupling agent providing for bonding between the resin and filler. Although there is a general listing of organic resins (e.g., acrylates) and inorganic fillers (e.g., clay) useful in binders, there is no suggestion of the advantages and disadvantages attendant with that combination of resin and filler. The examples utilize calcium metasilicate, calcium carbonate, and quartz as fillers.
Assignee's application Ser. No. 07/839,132, filed Feb. 20, 1992, now U.S. Pat. No. 5,269,821 (Helmin et al.) describes coatable mixtures including erodible filler agglomerates which are formed in situ and comprised of water-soluble and water-insoluble filler particles. During wet grinding operations, the water-soluble filler gradually dissolves. The agglomerates may be employed in many organic resins, including radiation cured resins. However, there is no teaching of the use of clay to provide a more erodible binder.
Microabrasive products have been commercialized since 1987 by assignee Minnesota Mining and Manufacturing Company, St. Paul, Minn., ("3M") under the trade designation "Imperial Beaded Microfinishing Film", which utilize as the abrasive surface grade 600 abrasive particles, clay, and a phenolic resin. While these products have enjoyed much success, the industry is continually seeking improved binder systems.
Some clays expand on exposure to water, while some do not (such as kaolin clay). See for example "Clay Colloid Chemistry", pp. 64-71 (1977). However, it appears the abrasives art is devoid of teaching the significance that clay fillers may have on the erodability of binders which include addition polymerized resins. This may be because past experience has revealed that in some instances when addition polymerized resins have been incorporated into abrasive articles, the binder does not sufficiently erode. If the binder does not sufficiently erode, the abrasive surface tends to dull and decrease in performance. It would thus be a significant advance in the abrasives art if binders incorporating addition polymerized resins would controllably erode.